1. Field of the Invention
The present invention relates to a vehicle air conditioning system mountable on a vehicle equipped with the control function of stopping a vehicle engine (internal combustion engine) automatically when the vehicle stops.
2. Description of the Related Art
In recent years, to benefit the environment and improve vehicle fuel economy, vehicles whose engines turn off when the vehicles stop (eco-run vehicles typified by hybrid cars) have been put to practical use. Eco-run vehicles of this kind are becoming increasingly popular.
Japanese Patent Laid-Open Publication No. 2000-179374 describes a driving control of a compressor in an eco-run vehicle which stops its vehicle engine automatically when the vehicle stops and addresses the case where a stopped condition of the vehicle engine coincides with a cooling command of the vehicle air conditioning system. Specifically, the publication describes a restarting of the vehicle engine to drive the compressor if the actual room temperature exceeds a passenger-determined passenger compartment temperature setting.
Since the foregoing publication does not mention that the compressor in the vehicle air conditioning system is a variable displacement type, the compressor is likely to be an ordinary, fixed displacement type. With a fixed displacement compressor, an electromagnetic clutch is arranged on a compressor pulley for transmitting engine rotation. This electromagnetic clutch is controlled in an on and off manner to switch the compressor on and off, whereby a cooling exchanger, or evaporator, is controlled with regard to temperature.
Nevertheless, the on and off switching of the compressor not only causes a shock but produces such problems that the temperature of the evaporator, or evaporator outlet air temperature, greatly varies. For this reason, luxury cars and other vehicles adopt air conditioning systems that employ a variable displacement compressor, configured and capable of continuous changes in discharge, to control the temperature of the evaporator.
The vehicle air conditioning systems using this variable displacement compressor are, however, not supposed to switch the compressor on and off, but are to keep the compressor operating continuously while adjusting the compressor discharge to control the temperature of the evaporator. Consequently, when a vehicle air conditioning system using a variable displacement compressor is mounted on the foregoing eco-run vehicle, and a stop condition of the vehicle engine coincides with a cooling command to the vehicle air conditioning system, then the vehicle engine sometimes must not be stopped. This results in a considerable decrease in the time possible for the eco-run vehicle to stop idling. The original effects of the eco-run vehicle, i.e., environmental protection and improved fuel economy then become impaired.
The present invention has been achieved in view of the foregoing. It is thus an object of the present invention to provide a vehicle air conditioning system mountable on a vehicle that has the control function of being able to stop its vehicle engine automatically while the vehicle is stopped (i.e. an eco-run vehicle). Additionally, the system will have a compressor that is driven by the vehicle engine and that is capable of changes in discharge capacity like a variable displacement compressor, and wherein engine stop time can be secured when the vehicle is stopped.
To achieve the foregoing object, a first aspect of the invention provides a vehicle air conditioning system mountable on a vehicle having a control function of issuing a stop request to a vehicle engine to stop the vehicle engine automatically when the vehicle is stopped. The system contains an engine driven compressor capable of changing its discharge capacity and an evaporator for cooling air to be blown into a passenger compartment. The evaporator is arranged on a suction side of the compressor. When the vehicle is running, the discharge capacity of the compressor is adjusted to control the evaporator temperature. When the vehicle engine stop request is issued when the vehicle is stopped, the discharge capacity of the compressor is kept at or above a predetermined capacity and the vehicle engine is either stopped or activated depending on the temperature of the evaporator. The temperature of the evaporator determines whether the compressor is turned on or off.
Specifically, in the first aspect, the discharge capacity of the compressor may be changed by various means. A variable displacement compressor may be used to change the discharge capacity, and a fixed displacement compressor, which is constant in displacement, may employ a transmission between the compressor and the vehicle engine. The transmission being capable of controlling a gear ratio by an exterior control signal to change the speed of the compressor.
According to the first aspect, when the vehicle is running, the discharge capacity of the compressor can be adjusted to favorably control the evaporator temperature with no great fluctuations. Additionally, the compressor power transmission system is prevented from a shock attributable to on-off operations.
When the vehicle is stopped, the vehicle engine is either stopped or started depending on the temperature of the evaporator (9). The temperature of the evaporator determines whether the compressor is turned on or off. The evaporator temperature, when the vehicle is stopped, can thus be controlled by turning the compressor on and off. This will ensure adequate passenger cooling. Even if the compressor needs to be operated for the sake of cooling (dehumidification) using the evaporator when the engine is stopped, the stop time of the vehicle engine can always be ensured because the compressor is controlled with its discharge capacity kept at or above a predetermined capacity. This ensures environmental protection and improved fuel economy which are the original aims of the eco-run vehicle.
Incidentally, the temperature of the evaporator to be detected or monitored is typically the outlet air temperature of the evaporator. Likewise, the fin surface temperature of the evaporator, the refrigerant evaporation temperature, the refrigerant piping surface temperature of the evaporator, and such, may be detected instead.
A second aspect of the present invention provides a vehicle air conditioning system according to the first aspect, wherein the predetermined capacity, when the vehicle is stopped, is a maximum capacity. In this case, the temperature of the evaporator can be lowered quickly within the operating period of the compressor so that the operating time (operating rate) of the vehicle engine, when stopped, is minimized to make best use of the original effects of the eco-run vehicle.
A third aspect of the present invention provides a vehicle air conditioning system according to the first or second aspect, wherein a temperature near a minimum temperature possible for the evaporator to be prevented from frosting while the compressor is turned on and off while the vehicle is stopped, is set as a first predetermined temperature (TE1). Additionally, a temperature sufficiently higher than the first predetermined temperature (TE1) is set as a second predetermined temperature (TE2), the temperature being an upper limit of a cooling temperature at which the increased temperature of the air blown into the passenger compartment starts to make a passenger feel uncomfortable. When the vehicle is stopped, the vehicle engine is activated when the temperature of the evaporator exceeds the second predetermined temperature (TE2), and is stopped when the temperature of the evaporator falls below the first predetermined temperature (TE1).
Consequently, the vehicle engine is not activated until the temperature of the evaporator exceeds the second predetermined temperature (TE2), i.e., the upper limit of cooling temperature at which the passenger starts to feel uncomfortable (in too hot or too humid conditions). The operating time of the vehicle engine can thus be effectively reduced while cooling is secured when the vehicle is stopped. Moreover, the vehicle engine, once activated, is kept operating until the temperature of the evaporator falls below the first predetermined temperature (TE1), which is the temperature near the minimum temperature possible before the evaporator generates frost. This prevents frequent activation of the vehicle engine when the vehicle is stopped in order to cool a vehicle passenger compartment.
In a fourth aspect of the present invention, the compressor uses a variable displacement compressor configured to be capable of changes in displacement. In this case, the displacement can be adjusted to exercise the operation and effects of each of the first through third aspects.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.